1. Field of the Invention
The present invention relates to a current control device for an inductive electric load which is used in, for example, an on-vehicle electronic control apparatus, and in particular, to a current control device for an electric load which is negative-feedback controlled by a target load current and a detected load current for improved current control accuracy.
2. Description of the Related Art
Various types of current control devices for electric loads are known, which control an on/off duty factor of a switching element connected between a drive power supply and an electric load such that a target load current coincides with a current detected by a current detection resistor. For example, such control devices include current control devices for linear solenoids which require a current constantly varying in a wide range, and current control devices for fuel injection electromagnetic valves which are kept open by a constant low current after being opened rapidly.
As one example of the current control devices, an internal feedback control type is known in which a microprocessor generates a target load current and a switching drive command in accordance with a deviation between a target load current and a detected load current (see JP2006-238668A (FIG. 1 and Abstract)). As another example of the current control devices, an external feedback control type is known in which a microprocessor only generates a target load current, and a switching drive command is generated by a deviation integration circuit provided outside the microprocessor in accordance with a deviation between a target load current and a detected load current (see JP2006-100509A (FIG. 1 and Abstract)).
The current control device for an electric load described in JP2006-238668A or JP2006-100509A includes a current detection resistor which is connected in series between a switching, element and an electric load, and an amplifier circuit part which amplifies a voltage across the current detection resistor by a differential amplifier to obtain a monitored voltage proportional to a load current. JP2006-238668A or JP2006-100509A describes a device in which sequentially, obtains calibration constants in terms of the causes of error occurrence so as to suppress control errors in the current control circuit as a whole.
Meanwhile, a semiconductor power module described in JP2005-033965A (FIG. 4 and Abstract) uses a bonding wire as a current detection element to measure a main circuit current flowing in a power semiconductor element by a voltage drop in the bonding wire. The semiconductor power module is also provided with a temperature sensor in which detects the temperature of a predetermined portion of a case in which forms the appearance of the semiconductor power module. JP2005-033965A describes a device in which accurately carries out current detection by a temperature correction circuit, which has a data table representing the relationship between temperature and resistance value of the bonding wire, even when temperature changes.